1. Field of Invention
The present invention relates to a gas concentrating method and apparatus using pressure swing adsorption (PSA), and more particularly, to a gas concentrating method and apparatus in which a high-pressure gas concentration is performed in a system (which means a two-adsorption-bed system, which is hereinafter referred to as a multi-bed system) where two adsorption beds (hereinafter referred to as sieve beds) alternately repeat concentration of a weak adsorption matter and washing of a strong adsorption matter, and then the two sieve beds are made to temporarily communicate with each other through a solenoid valve, at their bottoms, in such a manner that a high-pressure raw material gas moves from a high-pressure sieve bed to a low-pressure sieve bed to thus equalize pressures in the two sieve beds and perform washing and discharging of the two sieve beds.
2. Description of the Related Art
A pressure swing adsorption (PSA) process separates and concentrates a gas such as oxygen using a difference in an adsorption quantity of oxygen adsorbed to an adsorption material according to a pressure. Since the PSA process uses only compressed air and an adsorption material, it does not discharge a pollution matter and its use is easy. Thus, the PSA process has been widely used in a medical oxygen concentrator for long.
According to a concentrating principle, when compressed air is introduced and pressurized in a sieve bed filled with an adsorption material, a strong adsorption matter is adsorbed and a weak adsorption matter is concentrated. As a result, oxygen is left and separately stored as a product gas. After the product gas has been obtained, the strong adsorption matter adsorbed to the adsorption material is detached as inner oxygen and discharged externally to then be decompressed.
According to an oxygen separation principle, two sieve beds perform the above-described concentrating steps alternately. That is, the oxygen separation process includes four steps. Here, oxygen, which is a weak adsorption matter, is separated from a massive amount of nitrogen, which is a strong adsorption matter, in the sieve beds including zeolite which is an adsorption material.
Nitrogen of about 80% consisted in the air is adsorbed to zeolite more than oxygen be. Accordingly, when air is introduced in a sieve bed filled with an adsorption material, nitrogen is adsorbed to the adsorption material and oxygen in the air from which nitrogen has been reduced rises up to an exit located in the upper end of the sieve bed. The main component of the risen oxygen is composed of concentrated oxygen which is -a weak adsorption matter.
The above-described two-sieve-bed type, that is, multi-bed type oxygen separating apparatus is used as an oxygen separator. The oxygen separator includes an adsorption unit for separating nitrogen and oxygen from the air, an operator performing compression, storage and discharging of the air, a controller turning a valve on and off, and a frame portion accommodating the adsorption unit, the operator and the controller.
The oxygen separating apparatus adopts an oxygen separation method of repeating a process of supplying compressed air to a sieve bed filled with an adsorption material and adsorbing oxygen, and a process of detaching the oxygen adsorbed to the adsorption material, to thereby obtain necessary oxygen of a predetermined concentration. Here, part of the necessary oxygen obtained in the sieve bed is circulated into the sieve bed in order to perform a detachment process.
The adsorption process includes the steps of introducing compressed air through a predetermined adsorption material, adsorbing nitrogen which is a strong adsorption matter, and separating oxygen from the air. Here, once an adsorption step has been performed, the nitrogen adsorbed to zeolite which is an adsorption material should be necessarily separated (detached) from the adsorption material, in order to restore the original performance. This process is called a washing process, in which part of the oxygen adsorbed to the adsorption material is recirculated under a low-pressure state and detached therefrom, to restore an adsorption performance.
As described above, oxygen concentration and nitrogen washing are repeated to obtain concentrated oxygen of a predetermined purity.
An oxygen concentrating apparatus for concentrating oxygen through a multiple-bed type sieve bed was filed by the same applicant as shown in FIG. 1.
The oxygen concentrating apparatus includes a compressor 50 for compressing air, a solenoid valve 40 for controlling a supply of the compressed air, sieve beds 60-1 and 60-2 for separating nitrogen and oxygen from the compressed air supplied through the solenoid valve 40, an orifice 90 connected between the upper portions of the two sieve beds, an equilibrium valve 120 installed between the two sieve beds, making high-pressure and high-purity oxygen flow from the upper portion of the sieve bed to that of the other sieve bed, to be in equilibrium, counter-current preventive check valves 90-1 and 90-2, a storage tank 100, a pressure controller 70 and a needle valve 80. In FIG. 1, a reference numeral 10 denotes an air intake filter, a reference numeral 20 denotes an air intake muffler, and a reference numeral 30 denotes an air discharging muffler.
When the inner portion of a first sieve bed 60-1 is pressurized with the air, in the oxygen concentrating apparatus, nitrogen is adsorbed to an adsorption material from the air, and the other remaining concentrated oxygen is discharged. At the same time, in the case of a second sieve bed 60-2, an adsorption material to which nitrogen is adsorbed should be washed. Accordingly, part of the concentrated oxygen in the first sieve bed 60-1 is transferred to the upper portion of the second sieve bed 60-2 through an orifice 90 to then wash the inside of the second sieve bed 60-2. Then, oxygen of a high-pressure and high-purity is transferred to the second sieve bed 60-2 for a short time to keep the oxygen concentration in equilibrium between the first and second sieve beds and discharge the internal gas after washing. Here, the internal portion of the second sieve bed 60-2 has a considerable pressure resistivity.
Thus, in the case of the oxygen concentrating system, a compressor continues to operate at high pressure in the first sieve bed and a pressurized concentrated oxygen at high pressure is supplied to the inside of the second sieve bed which is at the low-pressure state through an equilibrium valve. As a result, the above-described oxygen concentrating system has the following defectives.
First, since the second sieve bed is washed with a high-purity of concentrated oxygen, a mechanical energy loss becomes large due to pressurization of a compressor.
Second, when the concentrated oxygen of a high pressure is supplied from the upper portion of the first sieve bed into the inside of the second sieve bed which is at the low-pressure state after pressurization, the second sieve bed is kept to be at the high-pressure state while discharging the air. As a result, air discharging noise becomes excessive.
Referring to FIG. 2 illustrating the above-described processes, according to a pressure curve of the first sieve bed, the pressure rises up to the point immediately before the concentrated oxygen in the first sieve bed is discharged, and then part of the high-pressure oxygen is supplied to the second sieve bed through the equilibrium valve 120, so that the pressure is lowered from 2.5 to 1 during about 2 seconds, which is shown as a pressure difference between {circle around (1)} and {circle around (2)} in FIG. 2. Here, the pressure equilibrium is made between both the sieve beds, and the second sieve bed is partially pressurized.
Thereafter, since a time between an intersection at which the pressure curves of the respective sieve beds cross (at a point at which the pressure is 1. 5 as shown in {circle around (3)} in FIG. 2) and the maximum pressure rise-up point of the first sieve bed becomes longer from about 100 seconds to 127 seconds by about 27 seconds, a mechanical energy necessary for operation of the compressor for generating compressed air is increased.
Also, the pressure is 2.5 at the time of equalization of the pressure between the first and second sieve beds, which causes noise to occur during discharging.
That is, the PSA process in the conventional multi-bed type system performs an equilibrium process through the upper portion of the sieve bed in order to heighten an efficiency, in which the high-pressure raw material oxygen is supplied from the upper portion of the high-pressure sieve bed to the low-pressure sieve bed and used as washing and pressure equilibrium. As a result, since the high-pressure and high-purity raw material oxygen produced in the upper portion of the first sieve bed is supplied to the second sieve bed as the oxygen for washing, the mechanical energy of the compressor needed during compressing the oxygen is lost.
In general, most of the energy used in an oxygen generator is an operational mechanical energy of an air compressor. That is, although the mechanical energy used for pressurizing the air is used for separating the oxygen from the air in the inside of a sieve bed, part of the mechanical energy is lost since oxygen is discharged through the air during washing.
However, in the case that the sieve beds communicate with each other at their bottoms not their tops, to thereby transfer the raw material oxygen, the compressed oxygen located at the bottom of the high-pressure sieve bed can be used for pressurizing the lower pressure sieve bed as the pressurization oxygen which is not the high-purity concentrated oxygen. As a result, the mechanical energy can be considerably restored.
To solve the above problems in the gas concentration and washing method of the conventional gas concentrator, it is an object of the present invention to provide a method of pressurizing, washing and discharging a low-pressure sieve bed with a high-pressure gas remaining at the bottom of a high-pressure sieve bed during a pressure equilibrium process after obtaining a production gas.
It is another object of the present invention to provide a gas concentrating method of reducing noise of a discharging gas at a low-pressure side, in which a pressure equilibrium time between two sieve beds is shortened during gas concentrating and washing processes, to thereby obtain an energy reduction effect in operation of a compressor, and perform washing and discharging at a lower pressure.
It is still another object of the present invention to provide a gas concentrating apparatus adopting a pressure swing adsorption system using a low purity high-pressure gas at the bottoms of sieve beds under the control of each solenoid valve, in which an equilibrium valve installed between the upper portions of the conventional gas concentrating apparatus for performing a pressure equilibrium is removed and a solenoid valve is installed for perform a pressure equilibrium at the bottom of each sieve bed.
Accordingly, the valves connected in a complicated way on the tops of the sieve beds are removed to thereby simplify the whole structure.
To accomplish the above object of the present invention, there is provided a gas concentrating method of keeping pressures in equilibrium through the bottoms of two sieve beds when a pressure difference between a pressurized pressure and a decompressed pressure is maximized in a multi-bed type sieve bed which operates alternately between pressurization and decompression. Here, for the purpose of achieving the pressure equilibrium through the bottoms of the sieve beds, the pressurization time is shortened by pressurizing the high-pressure gas at high-purity in the first sieve bed to thereby reduce the pressurized energy, and discharge the washing gas at a lower pressure in the second sieve bed.
According to another aspect of the present invention, there is also provided a gas concentrating apparatus using pressure swing adsorption (PSA), the gas concentrating apparatus comprising: an air intake filter for filtering the air in the atmosphere; a compressor; two sieve beds for adsorbing nitrogen; an orifice for assisting washing of the sieve beds and obtaining high-purity gas; check valves for preventing an inverse flow of the gas; a storage tank for keeping the purity of the gas to be constant and reducing change of the discharged flow amount; a pressure controller for maintaining the pressure of the discharged gas at a low pressure; a flow meter for supplying a predetermined amount of gas; a muffler for preventing noise of the discharged gas after washing; a 3/2 solenoid valve installed on the bottom of each sieve bed in order to achieve pressure equilibrium using the discharged air and recollect the mechanical energy; and a controller for controlling the solenoid valves and compressor to be turned on and off.
The gas concentrating apparatus using the PSA uses preferably a 3-port 2-way solenoid valve as each of the first and second solenoid valves.
The gas concentrating apparatus according to the present invention does not use high-purity oxygen for nitrogen washing and discharging but uses low-pressure oxygen at the closing stage of the pressurization in either sieve bed, in a gas concentrating method of a multi-bed type using two sieve beds in which a first sieve bed performs concentration and a second sieve bed performs washing and discharging, and then repeats the concentration and washing alternately.